This invention relates to toothed elements and their manufacture. In particular, it relates to optimize designing methods and machinery for manufacture of toothed gears and gear cutters, molds or dies without limitation to cylindrical or conical surface geometry of present gear-making machinery and related methods.
Gear efficiency, use-life and noise are affected by efficiency of conjugal engagement of gear teeth. Limitations on conjugate action in conventional gears result primarily from: (a) imperfect geometric structure of gear teeth and spaces between teeth necessitated by known gear-cutting hobs and milling machines, and (b) imperfections in gear-tooth surfaces that result from conventional hobbing and machining methods. In turn, imperfection of geometric structure of gear surfaces results from conventional geometry of hobbing tools and use of the same geometry in milling machines for cutting gear teeth. Since their inception about 150 years ago, hobs and the forms of gears they cut, whether these forms are cut with hobs or with milling machines directly, have been considered so preferable that major improvement on them or better gear-making means for making better gears have not occurred until this invention.
Present gear-tooth manufacture starts with analysis of limitations based on capabilities of present hobs and production machines and stays within these parametric limitations. With this invention, gear-tooth manufacture starts with analysis of geometry for optimization of gear-tooth contact for particular use conditions, proceeds to construction of a cutting tool that can cut the optimized geometry and then cuts the optimized gear-tooth geometry to provide far superior gears. For all types and forms of geared-tooth bodies, the optimized gear geometry can result in relative geometric perfection of gear teeth that increase efficiency, last longer and make less noise.
Some machines and methods have been devised to improve, to replace or to supplement present hobbing and milling of gears. But they have neither addressed nor solved basic structural problems with present gears, gear-making methods and gear-making equipment.
Examples of machines, methods and products of manufacture which are different than taught by this invention but related are described in the following patent documents. U.S. Pat. No. 4,981,402, issued to Krenzer et at. on Jan. 1, 1991, taught a computer-controlled machine for cutting bevel and hypoid gears without overcoming basic geometrical flaws of hobbing tools. Krenzer""s machine yields substantially the same structural gear forms cut by hobbing tools but with a reduction of surface imperfections caused by essential hobbing practices. U.S. Pat. No. 5,116,173, issued to Goldrich on May 26, 1992, described a method for utilizing machinery taught by the Krenzer et al. patent and other machinery having similar capabilities. U.S. Pat. No. 5,228,814, issued to Suwijin on Jul. 20, 1993, disclosed a hobbing machine that decreased shift in hobs but did not eliminate hobs or change their structure to overcome geometrical limitations of hobbing tools. U.S. Pat. No. 4,038,732, issued to Hunkeler on Aug., 2, 1977, taught a large face-mill cutting tool for making large-diameter gears, but perpetuated geometrical problems of both milling and hobbing of gears. Other known prior art is not sufficiently related or similar for comparison.
In light of problems that have existed and that continue to exist in this field, objects of this invention are to provide a design and manufacturing method for toothed bodies and a manufacturing process which:
Provide optimum gear-tooth design for all types of toothed bodies;
Provide methods for making gear-tooth cutters for all optimum gear teeth;
Maximize efficiency and use life of all types and forms of gear teeth;
Minimize noise of all types and forms of gears and gear pairs;
Provide methods for manufacturing idealized geometry of all types of toothed bodies;
Provide special machinery and tools for manufacturing conjugate action gears with idealized geometry of gear teeth;
Provide method for design of variable diameter gears with idealized geometry of gear teeth;
Utilize newly developed mathematical laws governing movement of a cutter relative to a work piece to ensure conjugate relation of motion between gears of a manufactured gear pair. These mathematical laws defines the necessary relationships between the tooth pitch, pressure angle and spiral angle for optimized surface geometry;
Provide means and method for compensating for anticipated errors in manufacturing, assembly and operations of the gears;
Provide means for design and manufacture of spiral non-circular gear pairs having varied spiral angle for optimized conjugate motion;
Provide a varied-diameter cutter that is designed and manufactured to produce tooth surfaces with wide variations of sizes;
Provide a preferred embodiment of a hypoid cutter pair as a means for varying diameter or pitch of idealized hypoid gear pairs;
Provide a mold or die designed and manufactured for production of an optimized gear pair;
Enable a wide variety of functional relationship between input and output motions of gear bodies;
Accommodate errors and misalignment in design and manufacture for improved contact and noise reduction;
Allow design and manufacture of a wide variety of spiral non-circular gear pairs;
Allow selection of any number of teeth from one to large numbers; and
Allow wide flexibility in face width, shaft angle, center distance, pressure angle and tooth geometry for all types and forms of gear sets.
This invention accomplishes the above and other objectives with a method of gear design which perfects design of gear teeth instead of limiting gear-tooth design to present cutter geometry and manufacturing methods. A pair of varied- diameter cutters, such as hypo id cutters, are structured with a cutter having a geometric form that generates a perfected gear-tooth design as an example. Structures of the hypoid or other varied-diameter cutters are achieved with a cutter tool having a design cross-sectional shape of an idealized space between gear teeth on both of a pair of cutters. The cutter tool is reciprocated in shaping or machining relationship to hyperboloidal or other cutter blanks in design rotation on cutter axes. The cutter axes have variable heights above the cutter tool. Simultaneously with shaping or machine cutting either cutter blank, angle of reciprocation of the cutter tool and height of center of the cutter axes are varied designedly. Appropriate cutting edges are then formed on or attached to the varied-diameter cutter so formed. Pairs of gear blanks are then cut to perfected gear form by the pair of varied-diameter cutter tools. The same method and machine used for making varied-diameter cutters can be employed for cutting gears directly.
An apparatus of the present invention comprises a numerically controlled milling machine useful in forming variable diameter toothed gear pairs. The milling machine includes a frame, a headstock carriage carried by the frame and controllable for vertical travel on a head-frame face of the head frame, a machine spindle for carrying a workpiece, the machine spindle extending horizontally from the headstock carriage and operable for selectively controllable rotation of the workpiece, a cradle rotatably carried by the frame, and a machine carriage moveably carried by the cradle, the machine carriage controllable for rotational and reciprocal movement. Further, cutting tool holding means are carried by the machine carriage for holding a cutting tool therein during cutting contact with the workpiece, and control means are provided for numerically controlling operation of the milling machine in response to a preselected control input. The input includes cutting tool movement commands for providing a conjugate movement between toothed gears of a toothed gear pair to be manufactured.
A method aspect of the present invention includes a method for manufacturing a toothed gear pair, each toothed gear having a variable diameter and variable pitch for providing a conjugate action therebetween. The method includes the steps of providing a numerically controlled milling machine having a frame, a machine spindle having selectively controllable rotation for rotatably carrying a workpiece to be machined, a carriage moveably carried by the frame for rotation and reciprocation thereof with simultaneous rotation of the workpiece, and a cutter carried by the carriage for cutting the workpiece in response to a preselected control input, and providing a preselected control input to the numerically controlled milling machine, which input includes cutter movement commands for providing a conjugate movement between toothed gears of a toothed gear pair to be manufactured. A first variable diameter shaped workpiece is mounted on the machine spindle of the milling machine for rotation about an axis, the first variable diameter shaped workpiece having a minor diameter end and an axially opposing major diameter end. One groove is cut into the first variable diameter shaped workpiece by reciprocating and rotating the cutter, while simultaneously rotating the first variable diameter shaped workpiece about the axis in response to the preselected control input for providing a groove which extends along the surface of the first variable diameter shaped workpiece between the minor and major diameter ends. The first variable diameter shaped workpiece is then rotated about the axis by one circular pitch, in response to the preselected control input for providing a preselected number of teeth. The groove cutting and rotating steps are repeated for forming a first variable diameter gear-forming tool having the preselected number of teeth positioned between the grooves and extending from the minor to major diameter ends thereof, each of the teeth having a forming edge thereon, each of the teeth curved radially and axially outward while changing in pitch from the minor diameter end to the major diameter end. The first variable diameter gear-forming tool is then removed from the milling machine. A second variable diameter shaped workpiece in mounted on the machine spindle and similar forming steps are performed based on the preselected control input to fabricate a second variable diameter gear-forming tool. The first and second gear forming tools are then used to form first and second variable diameter gears in response to the control input, thus providing a toothed gear pair. In one embodiment, the first and second gear-forming tools are operable with a hobbing machine for forming the gear pair. In yet another method aspect of the present invention, the first and second toothed gears of the gear pair are formed using the numerically controlled milling machine as are the gear-forming tools. As will be described, one desirable variable diameter gear pair includes a hyperboloidal gear pair.